1. Field of the Invention
The present invention relates to a method for preventing overheating of a microwave oven.
2. Description of the Related Art
A microwave oven is a kitchen appliance based on a principle that generates heat via molecular motion of the food itself by passing microwave radiation at a frequency of about 2,450 MHz through the food within a metallic case.
In the microwave oven, when microwave radiation at the frequency of about 2,450 MHz is oscillated from a magnetron, and passes through the food in a cooking chamber, molecules constituting the food are charged to have a positive charge and a negative charge arranged at opposite sides thereof by the microwave radiation. At this time, the molecules have the positive charge at one side near a negative polarity of electric field created by the microwave beam, and the negative charge at the other side near a positive polarity of the electric field.
In this regard, polarity of electric field is changed two thousand four hundred and fifty million times per second, and causes severe collisions between the molecules, so that the food is cooked by heat created by the collision of the molecules of the food.
FIG. 1 is a constructional view illustrating a conventional microwave oven.
As shown in FIG. 1, the conventional microwave oven comprises a power terminal through which commercial alternating current power is supplied, a fan motor 50 connected with the power terminal to drive a cooling fan for cooling various electric components, a tray motor 60 connected in parallel with the fan motor 50 to rotate a tray of a cooling chamber, a high voltage transformer 70 connected with the power source to supply high voltage power to a magnetron.
In addition, a fuse 80 and a door switch 90 are connected in series between the power terminal and the fan motor 50 in which the door switch 90 is switched on and off according to opening and closing of a door of the microwave oven. A sub relay 30 is connected between the power terminal and the fan motor 50, and a main relay 40 is connected between the fan motor 50 and a primary coil of the high voltage transformer 70.
The microwave oven further comprises a controller 20 which outputs a control signal in order to control the main relay 40 and the sub relay 30 to be switched on/off according to a key signal input from a key input part 10. The sub relay 30 is switched on/off according to the control signal from the controller 20, and serves to supply or cut off the commercial AC power through the power terminal to or from the fan motor 50, the tray motor 60, and the high voltage transformer 70. The main relay 40 is switched on or off according to the control signal from the controller 20, and serves to supply or cut off the commercial AC power through the power terminal to or from the high voltage transformer 70.
In the conventional microwave oven, when the magnetron is continuously operated for a long period of time by supplying power to the high voltage transformer 70, various electric components of the microwave oven including the high voltage transformer 70 are liable to be overheated, and thus it is necessary to control an output level according to a cooking period of time.
However, the conventional microwave oven has a problem in that, since the output level is determined depending on the cooking period of time, the electric components can be damaged due to overheating of the microwave oven which can occur when an internal temperature of the microwave oven before or after cooking is not considered in the case where the microwave oven is continuously operated without a pause or with intervals of short pauses.